In orthopedic spinal procedures requiring the use of stabilizing or bone affecting instrumentation to correct deformities such as scoliosis, to treat trauma, or to achieve fusion, the use of rigid or stiff instrumentation is the current standard of care. This instrumentation, however, has many limitations.
First, it is difficult to use due to inherent stiffness, where the rods have to be rigid enough to hold the weight and deforming forces of a patient's spine in three-dimensional space. This level of rigidity makes it difficult to intricately contour the rods to fit the patient's anatomy.
Second, the rigidity of the rods limits the correction of a spine to that which can be achieved acutely in the short duration of an operation. The spine is a living, dynamic system that could potentially deform over longer periods of time compared to the brief time allowed in the operating room. Thus, if continuous forces could be applied for longer periods of time, greater correction could be obtained.
Third, spine constructs are often “over-engineered”, which can result in stress shielding (a reduction in bone density due to reduced physiological responses to impact) and/or adjacent level degeneration. Further, the existence or development of screw-rod-bone mismatches in rigidity can lead to bone failure (fracture).
Fourth, since instrumentation systems (rods and screws combined) are rigid and cannot tolerate many cycles of strain relative to the life of the patient, fusion of the spine is required. Thus, spines that perhaps could be treated with motion-preserving techniques currently require fusion to correct curvature.